Scattered jewels in the core of a cluster

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March 18 2011 7:00 AM

Scattered jewels in the core of a cluster

I love all the Hubble images of nebulae and galaxies, but sometimes you need a palate cleanser, an image clean and simple. Like one, say, full of the stars of NGC 288:

Phil Plait Phil Plait

Phil Plait writes Slate’s Bad Astronomy blog and is an astronomer, public speaker, science evangelizer, and author of Death from the Skies!  

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[Click to englobularclusternate.]

NGC 288 is a globular cluster, which are usually tightly-packed spheres of stars. NGC 288, though, is looser, with stars dispersed more throughout. This image from Hubble actually resolves the stars even in the core, where they tend to overlap in denser clusters. From 30,000 light years away -- half the diameter of our galaxy! -- this is a pretty decent feat.

The image is not exactly true color: blue is blue, but orange starlight is shown as green here, red represents near infrared light, and what you see here as orange is actually from the reddish glow of hydrogen. Confused? Yeah, sometimes astronomers color things oddly to make some characteristics clearer. In this case, the colors represent different mass stars. Medium mass red giants look yellow in the picture, and blue stars are more massive. The fainter stars are ones that are still happily fusing hydrogen into helium like the Sun does. However, those stars are much lower mass than the Sun, and have longer life spans.

And there's more: If you look carefully, you can see fuzzy orange objects poking through the stars. Those are distant background galaxies! They're probably hundreds of millions of light years away.

We think most globular clusters like NGC 288 form their stars all at once, making them really nice laboratories for studying how stars grow old and die. Since we can be pretty sure the stars are all the same age, it's one less thing we have to worry about when trying to understand them! Simplification can be nice... in science and in beauty.



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